In This Issue:
- Late blight updates for potato/tomato
- Cucurbit downy mildew updates
Amanda Gevens, Professor & Extension Vegetable Pathologist, UW-Madison, Dept. of Plant Pathology, 608-575-3029, gevens@wisc.edu
Late blight of potato/tomato. I’m aware of no new reports of late blight in the US this past week. Findings thus far in potato and tomato have been confirmed as US-23 Phytophthora infestans (still sensitive to mefenoxam/metalaxyl ie: Ridomil) in western NY and Ontario Canada. Here in Wisconsin, we saw limited accumulations of 5-7 DSVs across WI this past week. https://agweather.cals.wisc.edu/vdifn?model=late-blight. Please find a fungicide listing for Wisconsin potato late blight management: https://vegpath.plantpath.wisc.edu/documents/potato-late-blight-fungicides/
So far, we have not had any reports of late blight in tomato or potato in Wisconsin in 2025! I provide a season summary of late blight for 2025, with a review of the disease and its management in a series of slides to follow this article. Interestingly, there has been recent research indicating that the late blight pathogen can acquire resistance to mefenoxam (or metalaxyl) within a growing season. This further emphasizes the importance of early and thorough management of this disease. I acknowledge Dr. Katie Gold for her work on a few of the slides.
For custom values of P-Days (for Early Blight) and DSVs (for Blitecast for Late Blight), please explore the UW Vegetable Disease and Insect Forecasting Network tool for P-Days and DSVs across the state (https://agweather.cals.wisc.edu/vdifn). Fungicide details can be found in the 2025 Commercial Veg. Production in WI Extension Document A3422: https://cropsandsoils.extension.wisc.edu/articles/2025-commercial-vegetable-production-in-wisconsin-a3422/
Cucurbit Downy Mildew: No downy mildew was seen on cucurbits this past week at HARS, and none reported through our UW Plant Disease Diagnostic Clinic. There was a confirmed report of cucurbit downy mildew in South Carolina over this past week as reported through the Cucurbit Downy Mildew ipm PIPE website: https://cdm.ipmpipe.org/.